Study On The Impact Of Climate Change And Land Use Change On Runoff In The Middle And Upper Reaches Of The Heihe River

Climate change and human-induced land use change are the main drivers of water resources change in the basin.It is very important to analyze the effect of regional water resources change,identify the background of climate change and reveal the pattern of land use change for the development of regional socio-economic and natural ecosystem balance,and the quantitative differentiation of the contribution of climate change and land use change to surface water resources is an important element of regional sustainable development and The contribution of climate change and land use change to surface water resources is an important element of regional sustainable development and ecological security.In this study,the spatial and temporal variability of climate factors such as precipitation and temperature were determined,the climate change context of runoff change was identified,the spatial and temporal variability of land use pattern influenced by human activities was elucidated,and the contribution of climate change and land use change to the change of runoff in the middle and upper reaches of the Heihe River was quantified based on the Budyko hypothetical water-heat coupled model.The contribution of climate change and land use change to runoff changes in the middle and upper reaches of the Heihe River was quantified based on the Budyko hypothesis hydrothermal coupling model.The main conclusions are as follows:（1）The amount of surface water resources in the middle and upper reaches of the Heihe River continues to increase,instability increases,and the scientific management and rational allocation of water resources face great challenges.The annual runoffs of the Tailaihe River,the Hongshuihe River,the Fengle River,the Liyuan River,the Heihe River and the Babao River all showed fluctuating increasing trends,with incremental rates of 0.02×10⁸ m³·（10a）^-1、0.17×10⁸ m³·（10a）^-1、0.06×10⁸ m³·（10a）^-1、0.11×10⁸ m³·（10a）^-1、0.97×10⁸ m³·（10a）^-1 and0.28×10⁸ m³·（10a）^-1.The trend of increasing runoff accelerated significantly after 1990 and was most evident in the main stem of the Heihe River,where the increase in runoff occurred mainly in summer and autumn.The basin as a whole is dominated by abundant water years,flat water years and partial dry water years,with the three water years accounting for a total of 75.00%,74.60%and 72.90%of the overall.After 1990,the number of exceptionally abundant water years and abundant water years in the Heihe River has increased,and the phenomenon is more obvious in the source area and upstream,especially since 2010,the total water resources in the middle and upper reaches of the Heihe River have increased significantly.（2）Climate"warming and humidification"has become the main feature of climate change in the middle and upper reaches of the Heihe River,and the land use pattern is relatively stable.The incremental rate of precipitation in the middle and upper reaches of the Heihe River from1960 to 2017 was 0.82 mm/a,and the spatial variation pattern of seasonal change tendency rate was summer（0.41 mm/a）>autumn（0.30 mm/a）>spring（0.05 mm/a）>winter（0.04 mm/a）.The temperature increment rate was 0.04℃/a,and the spatial variation pattern of seasonal temperature change tendency rate was spring（0.044℃/a）>winter（0.041℃/a）>summer（0.033℃/a）>autumn（0.025℃/a）.The potential evapotranspiration showed a decreasing trend from 1960 to 1990 with a decreasing rate of-1.46 mm/a,and an increasing trend from 1991 to2017 with an increasing rate of 6.08 mm/a;the spatial variation pattern of the seasonal change tendency rate was spring（0.35 mm/a）>summer（0.23 mm/a）>winter（0.20 mm/a）>autumn（0.06 mm/a）.The characteristics of the quantitative changes of land use types from 1980 to2020 are specifically shown by the expansion of arable land,forest land and construction land area with 2.13%,0.07%and 0.60%respectively,and the shrinkage of grassland,water area and unused land area with 0.39%,0.01%and 2.40%respectively.The average values of single land use dynamic attitudes are arable land（0.63%/a）,forest land（0.03%/a）,grassland（-0.04%/a）,water（0.71%/a）,construction land（1.78%/a）and unused land（-0.17%/a）.（3）Climate change is the main cause of runoff changes in the Heihe River.The sensitivity of runoff to precipitation is highest at Yingluoxia station,followed by the lower bedding surface parameters and the lowest potential evapotranspiration.Budyko assumes that the hydrothermal coupled model is applicable to the analysis of attribution studies of runoff changes in the Heihe River with an error of only 3.1%.The contributions of precipitation,potential evapotranspiration and subsurface parameters to the runoff depth were 48.87 mm,-2.93 mm and-1.50 mm,respectively,with 109.98%,-6.60%and-3.38%,respectively,and the contribution of precipitation was the largest,followed by potential evapotranspiration,and the contribution of subsurface parameters was the smallest,indicating that climate change was the main cause of runoff changes in the Heihe River,which precipitation is the main factor.In summary,under the influence of climate warming and humidification and human activities,the spatial and temporal patterns,mechanisms and impacts of precipitation,runoff and evaporation processes in the middle and upper reaches of the Heihe River have undergone profound changes,and these major impacts on the hydrological processes and ecological and environmental effects in the region will gradually become prominent,and the scientific management and rational allocation of water resources will face great challenges.